The Role of milleri Streptococci in the Formation of Cariogenic Biofilm: Bacteriological Aspects

It is remarkable that the biofilm (adherence) mode of growth of bacteria on the tooth surfaces in the oral cavity has been well documented as one of the important causes of dental caries. This study has been undertaken to detect the ability of milleri Streptococci in the formation of bacterial cariogenic biofilm qualitatively and quantitatively by spectrophotometric assay with ELISA reader, and to detect, in terms of BICs and MBECs, biofilm antimicrobial susceptibility test for biofilm producer isolates of milleri Streptococci to ciprofloxacin. Forty swabs obtained from patients admitted to Operative Dental Clinic in the College of Dentistry in Al-Ramadi City were studied during the period from December 2009 to March 2010. Lancefield s group sero-grouping was done. Quantitative biofilm formation by spectrophotometric method was achieved. Antimicrobial susceptibility test for the study isolates at two physiological stages planktonic and sessile states was done. Out of 40 study specimens, 25 (62.5%) were culture positive cases. Among culture positive cases, 33 mixed bacterial infection cases were observed consist of both of Staphylococcus spp. and Streptococcus spp. while α-hemolytic Streptococci were identified as pure single culture in 25 (100%) cases. α-hemolytic Streptococci isolates which were submitted to Lancefield s group classification were identified as group F Streptococci. Out of 25 bacterial study isolates, 20 (80%) were biofilm producers distributed into 17 (68%) as strong biofilm producer and 3 (12%) as weak producer. In biofilm antimicrobial susceptibility test for sessile cells of Group F Streptococci against ciprofloxacin, the biofilm inhibitory concentration required were from (10X -100X MIC)μg/ml of this antimicrobial agent to inhibit bacterial biofilm. The minimal biofilm inhibitory concentrations from (100 X to 1000 X MIC) MICs μg/ml were enough to eradicate bacterial biofilm.It is concluded that most of group F milleri Streptococci isolated from patients with dental caries produced cariogenic biofilm. Also, in term of BICs and MBECs, the biofilm producer isolates were required 10-50 X MICs of ciprofloxacin to inhibit bacterial biofilm and 100- 1000 X MICs to remove of bacterial biofilm in patients with dental caries.